Mechanical begtifieb



0. A. RR/MEN:

MECHANICAL RECTIFIER. APPLICATION FILED APILZB, I9I5- 2 SHEETS-SHEET I.

Patented July 29, 191).

INVENTOR ATTORNEY UNITED STATES PATENT? OFFICE.

QUINCY A. BBACKETT, OFIITTSBURGH, PENNSYLVANIA, ASSIGNOR TOWESTXNGHOUSE ELECTRIC AND MANUFACTURING COMPANY, A CORPORATION'OF PENNSYLVANIA.

MECHANICAL RECTIFIER.

Specification of Letters Patent.

Patented July 29, 1919.

. Application filed April 29, 1915. Serial No. 24.745.

'liectifiers, of which the following is a specification.

My invention relates to mechanical current rectifier-s of the commutator type and it has for its object to providea device of the character described which shall be simple in design, efficient and reliable inoperation and capable of adjustment for sparkless commutation when supplying current to a load of variable electromotive force.

In the rectification of alternating current by means of mechanically driven commutating devices, it is somewhat difficult to obtain sparkless operation because of variations in the time of zero current flow when contact should be made or broken within the device. This is especially true when operating with loads having a variable counter E. M. F. or when operating with alternating-current waves of other than the sine shape. By my .a rotatable member driven in synchronism with the frequency of the alternating-current to be rectified and provided with a plurality of conducting are members of venous angular lengths corresponding to 180 elec' trical degrees or any desired portion thereof. A brush or brushes may be provided for closing the circuitwith certain of said contact making are members during the desired current wave,thc specific contact making arc member employed depending upon the back electromotive force o the load and the connections being such that, when the load has a. low back electromotive force, contact is made throughout the greater part of the current wave and, as the back clectromotive force of the wave increases, contact is made for successively decreasing portions of the current wave. M

In the,accompanying drawing, Figure l a diagrammatic view of a mechai dial rectifief and its attendant circuits constructed in accordance with my inveut-ion Figs, 2 and 3 are diagrammatic views of modifications of the rectifier shown in Fig; 1, and Fig. 4 is a graplr illustrating the operation of my invention.

Referring to the form of my invention shown in Fig. 1, a disk 5 is mounted to be driven by a motor 6 at half synchronous speedwith respect to the frequency of alternating current from a source 7. Are shaped conducting contact members 8' of different lengths are mounted on the face of the disk 5 and, symmetrically disposed with respect thereto, is a similar set of are shaped conducting contact members 9. The contact members 8 are connected together by suitable means 10 and are also connected to a contact making arc member 11, for a purpose to be hereinafter set forth. In a simi- 'lar manner, the contact members 9 are connectcd together by suitable wires 12 and also to a conducting arc member 13. Brushes 14 are mounted to bear respectively upon the contacting members 8 and are, in turn, con nected to one terminal of the alternatingcurrent source 7 through a. suitable switch ing device 15 and a load 16, such, for example, as a storage battery. Similar brushes 17 are mounted to make contact with the Brushes 19 and 20 are provided to make contact with the contact members 11 and 13 and are connected together by a suitable wire 21. Each of the switching devices 15 and 18 comprises a movable bridging member 22 and suitable fixed contact members 23. The two bridging members 22 are connected to a rod 24: of insulating material and are normally maintained in the position shown by suitable means, such, for example, as a spring 25 which draws the rod 24 against a. stop member 26. A core member 27 is mounted on the rod 24: and is associated with a solenoid 28 connected across the terminal of the storage battery 16.

Having thus described the structure of my invention, the operation is as follows: the disk 5 is rotated at such a rate that the length of the longestcontact members 8 and 9 and also the contact members 11 and 13 corresponds to substantially 1S0 electrical degrees. Under these conditions, with a back elcctromotive force in the battery 16 of such small amount as to fail to move the core 27, the circuit will be closed for alterhate waves of the desired polarity from the source I through the battery fibers h; the connecting wire 10, the contact member 11, brushes l9 and 20, with their connecting wire 21, the contact member 13, the co net-ting wire 12, all three of the contact members 9, the three brushes 17 and the switching device 18 to the other terminal of the source. During the remaining waves of the desired polarity,'the connections will be the same except that the contact meml) rs 9 and 13 are replaced by the contact members 8 and 11 and vice versa. It will thus be seen that the current path is made and broken for each wave at four distinct points in se ries connection, namely, at the brushes 1%, at the brush 19, at the brush 20, and at the I brushes 17. Furthermore, the current at the brushes 1-1: and 17 is permitted to flow in three distinct branches and, accordingly, any tendency to harmful sparking is minimized because of the minute sub-division of the energy tending to produce sparks. When sulficient back electromotive force is developed in the battery 16 to energize the sole-- noid 28 to such a. degree as to move the rod 2t against the spring and to disconnect the right. hand contact members 23 from the bridging members 2:2, the lonigest contact members 8 and 9 are'ren'ioved from the circuit. Contact is therefore made only'during shorter portions of each wave of the desired polarity because of the shorter length of the remaining contact members 8 and 9. This is the desired method of operation, as will be evident from a consideration of Fig. l wherein a line 29 "represents an alternating-currentwave of the desired polarity, the abscissa 30 representing the potential of the-battery at, the initiation of the charge nd the abscissa 31 representing the potential of the battery at a later point in the charging. The optimum point for closing the circuit through the rectifier is at the point of zero current flow, which is the point where therising voltage of the wave is exactly equaled by the back electromotive force of the battery. This pointis at 32 at the initiation of a charge and is retarded as the charge progresses, as shown by the point 33 corresponding to the increased battery voltage 3L In like manner, the optimum. moment for breaking the circuit occurs at 3 at the initiation of charg e and is advanced as the charge progresses, as shown by the point 35 corresponding to a battery moltage 31. Ordinarily, little orno ditlitiiilty is experienced with sparking; at the time of closing the circuit, and l have accordingly shown the. la ling ends of the contact memhers 8 and t) as terminating on the same ra dial line but, obviously, desiredflhe longest member may be made to close contact with the brushes Ll and 15 in advance of the other members. W'hen the volt-age of the battery 16 reaches a still higher figure, the core member 27 moves the ln'idging .members 22 to such an extent that only the' left hand cont-act members are engaged therewith, and only the shortest contact members 8 and 9 remain in circuit, with the re it tl t only asmall portion. of the wave a; the peak thereof is allowed to flow through the battery. Obviously, the number of contact members 8 and 9 may be increased to any desired degree in order to obtain more steps for the regulation of the mini mum alternating-current voltage allowed to tlow through the battery 16.

It is a well-known tact that the rate at which the ()Nllllll) lead storage cell can assimilate energy is much less toward the end of the charging period than at the outset thereof. Because of his fact, it is usual to taper off the charging rate, employing a much larger charging current at first than later on. By the. structure shown in Fig. l, a current path of relatively low brushqresistance is provided during these periods when relatively large portions of each wa-ve are rectified, that is to say. when the back electromotive force of the battery is low at the'ontset of the charging operation and, as the charge progresses with diminution of the charging current. the brush resistance of theicurrent ath may be increased.

Referring to the form of my in ent-ion 'shown in Fig. 2, a synchronous motor 8 is mounted to drive acylindrical drum 36 upon which are mounted sets of commutating segments 37 and 40 of varying lengths and corresponding auxiliary segments 38 and 39. The segments 39 and 40 are mounted with an angular displacement of substantially 1S0 mechanically with respect to the segments 37 and 38. All. the segments 32'' and 38 are con-- nected together by strap wires, as shown, in like manner, all the segments 39 and 40 are caused to act as a single conductive unit. A plurality of brushes ll to H, inclusive, are

mounted to cooperate respectively, with the contact making;- segn'ients 37 to 40, inclusive: The brushes 41 and llare connected, through v a hand operable switchaloflo the terminals of the secondary winding l6 of a transformer 47, the primary winding 18 of which s connected to a suitable source of altee nating current 49. The brushes -22 and 4 3' are connected together by a bond wire 50.

ine

and a. suitable load. such, for example, as a storage battery 51. is connected between the wire 50 and the mid point of the secondary winding 46. The synchronous motor 6 is designed to drive the drumBti zit-such speed that the length of the longer segments 37 and corresponds ,to nearly 180 electrical detees," f ",1 av'i'ng thus described the structure disclosed in Fig. 2, the operation is as follows: with the switching device 36 in the position shown, the brushes 41 to L4 corresponding,- respectively, to the longest of the segments 3'? and 40, are connected to the secondary winding 46. Assuming a positive wave to start from'the left hand terminal of the winding 46, it will pass through the switch- -ing device 45 .to the left hand brush 41.,

through the longest segment 87, thence through the strap wires to the segment 38, to the brush 42 and bond wire 50, and thence through the battery '51 tothe secondary winding 46. As the segments e0 are displaced by 180 mechanically with respect to the segments 37 on the drum 36, they will be out of contact with the brushes 44 during theabQve-described period of current flow. During the succeeding alternating wave, however, which will be positive at the right hand terminal of the secondary winding 36, the segments and 39 will make contact with the brushes 44 and 43, respectively, and current flow willbe permitted through the right hand half of the apparatus. In this manner, alternating-current waves of both polarities will be sorectifiedthat they will flow in the same direction through the storage battery 51 and will cause the voltage of the latter to rise. With the "rise of voltage in the storage battery, therewill bebrought timum time for the about a retardation in the optimum time of closing the circuit and opening thereof, as shown in Fig. 4. In order to prevent sparking, therefore, the operator manipulates the switching device {15 so that the contact making segments 37 and 40 ofmedium length are connected to the secondary winding 46 at the proper time, through the middle brushes 41 and 44, with the consequent proper adjustment of the time of make and break. In like manner, when the voltage of the storage battery is approaching a maximum, the switching device &5 is again manipulated so that the shortest segments 37 and 40 are included in circuit with their cor responding brushes.

Referring to the form of my invention shown in 3, which is in many respects similar to that shown in Fig. 1, a disk of insulating material is so mounted as to be driven by a synchronous motorvfi at half synchrcnism with respect to the frequency of the alternating current to be rectified. A c-tauducting member 53 is mounted. on the face of the disk 52, and, arranged to coact therewith, are brushes 55-55, mounted to slide in a suitable fixed frame 56 which is placed in front of the disk Bcllcrank levers 57 and 58 are mounted on suitable pivots 59 and 66, carried by the frame 56, and the bell-crankleversb? and 58 are each connected to the core member 61 of a solenoid 62 connected across a storage battery an advance in the opsuitable spring 65, throwing the brushes 5% and 55 outwardly so that they make contact with the rotating member 53 throughout relatively long arcs, current flowing from the brush 5:) to the member 53, thence through the neck thereof to the brush 5% and through the battery 63. Each end of the contact member 53 subtends an angle of slightly less than 90,with respect to the center of the disk 52, at the outermost arcof travel of the, brushes 54. and 55 and, therefore, when the disk 52 is driven at half synchronous speed by suitable design of the motor 6, the circuit will be closed through the battery 63 during waves of one polarity andopen during waves of the other polarity. As the charge of the battery 63 proceeds, the voltage thereof will rise, the strength of the solenoid 62 will increase, the core 61 will be drawn down and the brushes 54 and 55 will be gradually shifted toward the center of the disk 52, with conse' quent shortening of the arcs of contact with the member 53 and adjustment of the points of make and break in accordance with the principles set forth in connection with Fig. l.

While I have, for the sake of clearness,

shown the contact making are members in Figs. 1 and 3 asmounted on the-face of a rotating disk, it will be readily apparent to those skilled in the art that they may be mounted on the surface of a cylinder by suitable modification, without departing from the spirit of my invention, and a somewhat better design from a mechanical standpoint be secured. Furthermore, by a duplication of the contact making devices shown in Fig. 3 and by a suitable fixed phase relation between the two sets of contact makmg devices, both waves of alternating current may be rectified in the manner indicated in F 'lhroughout this case. I have described the operation of the moving rectifying memher at half-synchronous speed but its operation will be equally satisfactory if any even multiple or traction of syncln'onous speed be chosen, provided a proper numbcrof,sui*- ably proportioned contacting segments be 125"" employec For a rectifier adapted for general application, Whcre operation unloads having no back elcctromotive force may be desirable, it is necessary that the longest contact segments in my device cover substantially 180 electrical degrees, but, if only battery charging" operation is contemplated, the longest of the contact arcs need cover only so many electrical degrees as correspond to the time during which the applied electro-motive force of the load is equal to, or exceeds, the minimum back electromotive force of the load.

lVhen operating under heavy load, the capacity of a simple multiple-contact relay, such as is shown at 28 in Fig. 1, may be e ceedcd, and any suitable hoary-current control system may be employed, such for eX- ample, as a standard circuit breaker having its contacts in with each brush, each circuit breakere'being t 'ippcd by its own separately adjusted over-voltage coil.

While l have shown my invention in three distinct embodiments thereof, 1 do not de sire to be restricted to these embodiments but desire that only such restrictions shall be placed thereupon as are imposed by the prior art or are specifically set forth in the appended claims.

I claim as my invention:

1. In a commutating rectifier, the combination with a rotatably mounted member, of means for rotating said member in synchronism with the frequency of the altenating current to be rectified, com-J making means mounted upon said member and arranged to provide a plurality of contact making arc members of difi erent angular lengths, connections from said contactmaking means to one terminal of the source of alternating current to be rectified, means fo periodically connecting any one of said contact making are members to the other terminal of said alternating-eurrent source, and a load in one of said connec ions.

ln a commutating rectifier, the combination with a rotatably mounted member, or" means for rotating said member in synchronism with the frequency of the alternating current to be rectified, contact making means mounted upon said member and arranged to provide a. plruality of contact making are members of different angular lwig'ths, connections from said contact making means to one terminal 1 the source of alternating current to be rectified, a load of variable back E. M. F. between the alternating-current source and the rectifier, and means for periodically connecting the loi est of said contact making are inen'ibers the other terminal of said alternatinq-current source when the back M. of said load is at a minimum mine and for periodically connectingishorterand shorter contactma'king are members to the alter11atingcu1- rent source as the back M. F. of the load rises.

3. The combination with a source of alternating current, of a. commutating rectifier comprising rotatably mounted member, means for rotating said member in synchronism with the frequency of the supplied current, a. pluralityof contact making are members of dillerent angular lengths mounted upon said rotatable member, a plurality of fixed brushes, one 0;? which is mounted to make contact wi h each of said contact making are members, a connection from all of said contact making are members to one terminal of said source, a connection from the other terminal of said source to a switching device associated with said brushes, a load oi variable back E. M. l in one of said connections, and means operated by the back E. M. F. of said load to adjust said switclr ing device, whereby said last named connection is completed to arious of said brushes in accordance with the iolta'gc of the load.

et. The combination with a source of alternating; current, of a commutating rectifier comprisinga rotatably mounted member, means for rotating" said member in synchronism with the frequency of the supply current, a plurality or contact making are members of different angular lengths mounted. upon said rotatable member, longest of said members covering substantially 180 electrical degrees and the remaining are members diminishing in length therefrom by graded amounts, a' plurality of brushes, one of which. mounted to r ake contact with each of said contact making are menu hers, a connection from all or" said contact makin ;1' are members to one terminal of. said source. a connection from the other terminal of said source to a hing device associated with said brushes, a load of variable back M. F. in one of said connections, and means operated by the back M. F. of said lead to adjust said switching device, whereby said last named connection is compl'etcd to the brush in contact with said longest contact making arc member when said back E. M. F. is at a minimum value and is completed to shorter and shorter contact making are members in accordance with increases in the back '3. id. F. or the load.

In testimony whereof I have hereunto subscribed my name this 245th day of April, 1915.

(31 A. BRACKETT. 

